A typical electric vacuum cleaner is provided, at one end of a tube connected with its motor, with means for collecting dust (hereinafter referred to as dust suction head). The suction head has a rotational brush adapted to collect dust on a floor while air is sucked by the motor from a dust suction port of the head. The brush is driven by an electric motor or a turbine.
However, such head is heavy and very complex in structure, so that it not only has limited portability but also requires many parts and complicated processes for assembly.
In a vacuum cleaner having a turbine for rotating the brush, the turbine is normally installed in a turbine chamber formed in an air passage en route from the dust suction port of the head to the air outlet of the head, so that the turbine is rotated by the air flow through it. As a result, dust can accumulate in the turbine chamber, hindering the rotation of the turbine.
In order to overcome these problems, a new rotational brush was disclosed in such early Japanese patent publications as No. 9-28630. The brush has two turbines mounted on the opposite ends thereof. The turbines are rotated by fresh air taken into the chamber. The fresh air is then taken into the vacuum chamber together with the air sucked from the dust suction port of the head.
In this arrangement, since the two turbines are required on the opposite end of the rotational brush, they require a number of extra parts and must be designed so as not to loose dust suction power even while much air is sucked to rotate the two turbines. In other words, the turbines must be designed so that is can rotate by a small amount of air. However, such turbines are likely to fail to rotate at a desired speed when the head is placed on a resistive carpeted floor, for example. Furthermore, the dust suction port formed in the bottom of the turbine chamber is limited in length, since it is difficult to form a dust suction port right under the turbines. As a result, the head, having a much smaller width than the dust suction head, can sweep only a limited area of the floor, leaving dust behind it.